HALLANDALE, Fla. — Doug Donn, president of Gulfstream Park since 1978, whose family has run this racetrack since 1944, yesterday stepped down from his day-to-day responsibilities, effective Friday.

David Romanik, an attorney for Gulfstream since 1976, its chief counsel since 1982 and a prominent thoroughbred owner-breeder, was appointed the new president and general manager by Frank Stronach, chairman of Magna Entertainment Corp., which purchased Gulfstream in September for $95 million.

Donn, who was named chairman of Gulfstream, said he will devote much of his time to easing government regulations that control the racing industry.